Fast idle while driving?

Thanks very much for your answer. I will take a look at it, though I'm not very 'engine savvy, ' so might take it to a mechanic we have here. I've already had one look at it, but they were unable to solve the problem, so that's why I was writing to see if there might be something they haven't tried. I will let you know how it goes, but it might be a while till I can get to it. Thanks again for writing.

Actually, what I'm going to do first is look through my receipts and see if I can determine what was checked so far. I'll let you know what I find.

I originally took the car in because it had a service engine soon light, and it was idling fast all the time (even when stopped in gear at an intersection). On that visit, they did the following:

Scan the vehicle for codes.
Clear codes: Lean 44
Check for vacuum leak, fuel pressure
Tighten side cover on transmission, adjust spring tension (had catch)
R&R Throttle position sensor, clean throttle body
R&R Mass air flow sensor
(+the usual oil change etc.)

When I got the car back, it seemed better. The service engine soon light was off and it idled slow when first starting and had a slow idle at stop lights, but something seemed off while driving and eventually I realized that the idle was bumping up fast as soon as the gas was applied with the car in gear. It made the car drive itself at about 30mph in 3rd and harder to stop. But once stopped the idle wound down to a slow idle, until the gas applied again. It doesn't happen in neutral (After starting one can step on the gas in neutral and it returns to a slow idle. It only happens in forward gear. I had read online that maybe unplugging the power to the computer and resetting might fix it so we tried that, but it didn't help.

I'm just wondering if you can think of anything else that might cause this. Did it sound like they did the lubrication you mentioned in your first post? Though would that problem affect the idle in both neutral and forward?

Thanks, John

They also replaced the oxygen sensor on that first visit.

Thanks much for your thoughts. I'll try to check it in the next few days with a helper.

Hello again. I actually did more testing and the problem does happen in neutral. For example, if, as I'm driving and the car is idling fast, I put it in neutral, it continues idling fast until it rolls (or is braked)to a stop. Just after it stops, the idle will go down to a slow idle. But as soon as the car starts rolling again, the idle speeds up. It does it in gear and in neutral both.

Thanks very much for all the suggestions here and in the link. I will bring this up with my mechanic and see what happens.